Vegetable oils are typically oils that have been pressed or extracted, such as from a vegetable source. Many vegetable oils contain some form of phosphatides (e.g., hydratable or non-hydratable), commonly known as gums. For instance, soybean oil contains about 1-3%, corn oil 0.6-0.9%, sunflower oil 0.5-0.9%, and canola oil (crude) 1-3% of gums.
Gums can be partially or totally removed from vegetable oils through several different known degumming processes. The most commonly used processes in the industry are water degumming, acid degumming, caustic refining and enzymatic degumming, for example, as disclosed in U.S. Pat. Nos. 4,049,686; 5,239,096; 5,264,367; 5,286,886; 6,001,640; 6,033,706; 7,494,676 and 7,544,820, and U.S. Pat. Pub. Nos. 2007/0134777; 2008/0182322 and 2012/0258017.
A method disclosed in U.S. Pat. No. 4,240,972 discloses adding an acid to a heated stream of crude vegetable oil and then immediately passing the mixture through a static mixer to produce an acid-in-oil dispersion, and then separating the dispersion into an oil phase and an aqueous phase containing the phosphatides. In another example, U.S. Pat. No. 4,698,185 describes a vegetable oil refining method with the steps of dispersing an aqueous organic acid in a water-degummed oil to form an acid-in-oil dispersion, allowing the phases to remain in contact for a time sufficient to decompose metal salts of phosphatidic acid, adding a base to the acid-in-oil dispersion to increase pH to above 2.5 without substantial formation of soap, and finally separating the dispersion into an oil phase and an aqueous phase containing the phosphatides.
U.S. Pat. Nos. 4,698,185 and 6,015,915 describe processes for degumming vegetable oil using a high shear Ultra-Turax rotor/stator apparatus. U.S. Pat. No. 6,172,248 describes a method for refining vegetable oils and byproducts thereof. In an organic acid refining process, vegetable oil is combined with a dilute aqueous organic acid solution and subjected to high shear to finely disperse the acid solution in the oil. High shear rotor/stator apparatus are known to be used to generate hydrodynamic cavitation in fluids.
Cavitation has a tendency to release dissolved gases in an oil mixture and generate post cavitation gas fields of tiny bubbles in the fluid flow. Those bubbles become coagulation centers for the soap stock particles, entrap oil in the larger agglomerates and can decrease phase boundary in the oil-acid/base solution. As a result, the rate of hydrolysis of phosphatides, and the degree of removal thereof, in the purification process will decrease as the fields of bubbles persist in the fluid. Entrapment of the oil in the larger agglomerates can also increase oil yield losses.
A method disclosed in U.S. Pat. Pub. No. 2009/0314688; 2011/0003370, and 2014/0087042 involves mixing crude oil with degumming agents, e.g., water or acid, and passing the mixture through a hydrodynamic cavitation device. Numerous flow-through hydrodynamic apparatuses are known, for example, those disclosed in U.S. Pat. Nos. 5,810,052; 5,971,601; 5,969,207; 6,035,897; 6,502,979; 6,705,396; 7,338,551 and 7,207,712.
Cavitational processing provides the highest shear to oil degumming processes but at the same time extracts dissolved gases from liquids and generates post cavitation gas fields of tiny bubbles in the flow. Accordingly, there is a continuing need for a method for degumming that can provide the highest shear to the process but at the same time eliminate the cavitational degassing problem observed in known methods.